Carrier Water Explained/Usage 2

[ohiowater]

I am trying to gather a reasonable engineering explanation as to what truly dictates the use of carrier/feed water in chemical feed applications at Water Treatment Plants. This really seems to be somewhat indiscriminant amongst engineers.

Is the basis:

- Distance to the chemical feed point from the metering pump?
- The type of chemical being fed?
- The quantity of chemical being fed?

I have heard some clients and engineers say the use of carrier is simply a judgement call. I have heard some say provide carrier water for every chemical regardless of the constraints/applications. I have never heard or read any specific engineering feedback when to use, why, and how to size.

For example......

- Is 1/2" water connection always enough or is too much, this seems to be a common size.
- Should the carrier water always be sofetened or just with select chemicals that tend to scale or crystallize such as Sodium Hydroxide? Others?

Any engineerinhg feedback, references or resources would be greatly appreciated.

 

[bimr]

In feeding soluble chemicals such as aluminum sulfate, soda ash, etc., the usual concentration is also 5% and seldom exceeds 10%.

The practice of using carrier water to transport chemicals is based on plant experience. The intent of the carrier water is to minimize problems of chemicals plugging lines, freezing of the various chemicals, solids depositions in piping, reducing corrosion from treatment chemicals, reducing delivery time from chemical tank to process, improving dilution, etc.

Carrier water only needs to be softened if you are adding an alkali that will cause the dissolved solids in the water to precipitate/scale and the resulting precipitate/scale causes problems with the process.

The practices are rules of thumb based on operating experience. All the practices can be are rules of thumb because you are dealing with all types of water quality, chemicals, processes, climate, and materials of construction depending on the application.

 

[rcooper]

Removing carrier water from a design can cause problems with mixing. I've had to sort out problems arising both with static mixers and weir mixing when carrier water has not been used. It wasn't impossible, but having carrier water helps a lot with the mixing, especially when the mixing has to be carried out quickly (such as coagulant dosing).